Mr Diamond is making the bid through his private equity firm Atlas Merchant Capital, alongside Qatari bank QInvest, which holds around 43% of Panmure.

The deal, for 100p per share, values Panmure at £15.5 million and represents a 68% premium.

Panmure’s board has recommended the offer to shareholders who will vote on the deal.

The group said in a statement that Panmure’s board “unanimously consider the cash consideration to be fair and reasonable” and that it already has the backing of 60% of investors.

Once complete, the deal will see Panmure, one of the country’s oldest stockbrokers, delisted from the London market and taken private.

The move marks a comeback for Mr Diamond, who quit Barclays after the bank’s £290 million Libor-rigging settlement in 2012.

Mr Diamond was regarded at the time as a brash American investment banker - once described by Lord Mandelson as the ‘’unacceptable face of banking’’ due to his lavish pay deals - a tag that ended up tarnishing Barclays as it became embroiled in the Libor sandal.

Matthew Hansen, the UK head of Atlas, said: “We believe there is significant opportunity for Atlas, in partnership with QInvest, to apply our operational skills and financial services expertise to enhance Panmure Gordon’s strong reputation and build a larger, successful boutique investment bank.

“This long-term stabilisation and development can only realistically be achieved as a private company, out of the glare of the public market and the effects of share price movement.”